Adsorbent

ABSTRACT

An adsorbent that can be used to remove environmental contaminants such as organics, cations and anions in a single process step is prepared from humic acid. The adsorbent can be a soluble humic acid in liquid form (e.g., in aqueous solution) or the humic acid can be insolubilized and/or immobilized on a solid support. The adsorbent can also be used to recover agriculturally desirable metals in chelated form from contaminated water. The liquid form of the adsorbent can be used to wash solids to remove contaminants.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application no. 08/698,122,filed Aug. 15, 1996, now U.S. Pat. No. 5,906,960 which claims priorityfrom provisional application 60/002,378, filed Aug. 15, 1995, the entirecontents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention is directed to an adsorbent based on humic acidwhich can be used to remove metals, radionuclides, and/or organicmaterials generally present as environmental contaminants at a varietyof sites.

BACKGROUND OF THE INVENTION

Heavy metal and organic contamination of soils, buildings and equipmentsystems is a major environmental concern at both industrial andgovernment sites. The contamination is primarily due to improperlydisposed industrial wastes. The presence of toxic heavy metal ions,volatile organic compounds and pesticides in the environment is of greatconcern and could affect worker safety as well as the safety of drinkingwater and air for the general public.

Federal and state pollution control standards for heavy metal content ofmineral-producing discharges and for other types of waste disposal havebecome increasingly stringent. In addition, acid mine runoffcontaminated with dissolved metals from abandoned mines contributes toenvironmental degradation. Other sources of contamination includedischarge from federal facilities, e.g., military weapons complexes,which are a source of metals, organics, and radionuclides. Additionalsources of contamination include oil and gas exploration and productionoperations. Where dissolved metals must be removed from such a wastestream prior to discharge, precipitation is the most common method,generally precipitating the metals by adding calcium oxide. Althoughcalcium oxide addition is relatively simple and cheap, this methodresults in a great volume of sludge which is costly and hazardous todispose of. Moreover, because of incomplete reaction, the effluent isoften not completely removed from the water, and the metal values arenot recovered and are thereby wasted. Also, the precipitation layer insettling ponds undergoes an inversion at temperatures around 4° C.

Many waters are contaminated with mixed wastes, which conventionally aretreated with activated carbon followed by elution through ion exchangeresin columns. Because these two methods operate on differentprinciples, both technologies are applied sequentially, rather thansimultaneously. This conventional technology is very expensive andcumbersome to use.

In Bureau of Mines Report of Investigations, 9200, Pahlman et al.describe the use of lignochemicals and humic acids to remove heavymetals from process waste streams. The sodium salt of lignin and thehumic acids of peat, lignite, and subbituminous coal were found to beexcellent at removing the more toxic heavy metal ions, including Cd⁺²,Pb⁺² and Hg⁺², while calcium oxide addition was found to be poor to fairfor their removal. However, the coagulability of the heavy metalsequestrates of the lignin sodium salt at pH 7 makes removal lessefficient and causes difficulty in filtration.

Pahlman et al. found that a mixture of three humic acids has aparticular affinity for Cd⁺², Hg⁺² and Pb+2, and can be used to effectalmost total removal of these ions from waste streams. The humic acidsused were prepared by caustic treatment of a North Dakota lignite, aMontana subbituminous coal, and a Minnesota peat.

Alexander, in U.S. Pat. No. 5,034,045, describes a method for improvingagricultural crop yields using a mixture of a water-soluble alkali metalsalt of humic acid and plant nutrient components such as nitrogen,potassium, and/or phosphorus. In this case, the oxidized sites of humicacid are filled with non-volatile alkali metal ions that maintain thewater solubility of the humate salt used.

Moran, in U.S. Pat. No. 4,459,149, discloses a process for treatinghumus materials comprising freeing humic acid from the combined state inwhich it frequently exists in humus materials, dispersing it as a fine,insoluble solid in acid process water, separating it from the impuritieswith which it is associated, and recovering it as a high solids filtercake. The humic acid can be solubilized by mixing with solubilizingagent such as alkaline salts and the like. Insoluble humates areobtained by adding a metal compound to a humate solution.

Muir, in U.S. Pat. No. 4,952,229, discloses a soil and foliar supplementfor plants comprising a quantity of specific microbes and an organicacid such as humic acid, fulvic acid and ulvic acid, along with optionaltrace minerals and chelated micronutrients.

Although activated carbon is very effective in removing organiccompounds, it is associated with high capital and operating costs,especially when regeneration is effected by the most effective process,thermal reactivation. Also, this technique is very sensitive to thepresence of suspended solids, oil and grease, requiring pretreatment foreffective performance.

Although conventional means for decontaminating surface and groundwaterinclude a broad spectrum of treatment options such as precipitation,ion-exchange, microbial digestion, membrane separation, activated carbonabsorption, etc., the state of the art technologies can in one passremediate only one class of contaminants, i.e., either volatile organiccompounds using activated carbon or heavy metals using ion exchange.This requires the use of at least two different stepwise processes toremediate a site.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome the aforesaiddeficiencies in the prior art.

It is an object of the present invention to provide an adsorbent whichadsorbs anions, cations, and volatile organic compounds fromcontaminated objects and sites, such as from water, equipment,buildings, soil, ground water, oil and gas exploration and productionsites, and similar sites.

It is another object of the present invention to provide a method toremove organic compounds, metal ions, and anions when present, eithersingly or in combination, from waste, process, or runoff streams.

Another object of the present invention is to recover agriculturallyvaluable metals from contaminated waters and to market the metals aschelated micronutrients.

Still another object of the present invention is to recover commerciallyvaluable metals from contaminated waters.

According to the present invention, a sorbent is provided that can beused to treat organic compounds, or both organics and metal ions in asingle process step or in a series of steps. As compared to conventionalmethods of reclamation, which include separate steps using, e.g., bothcarbon adsorption and ion exchange resins, the process of the presentinvention is less expensive and easier for treating all types of processstreams.

The adsorbent of the present invention is based upon humic acid. Thehumic acid may be used either in a water soluble or water insolubleform, depending upon the contaminants to be removed, the concentrationof the contaminants, and the use to which the adsorbent/contaminantscomplex is to be put. If the water stream to be cleaned contains metalions useful for agricultural purposes, such as iron, zinc, copper,boron, manganese, magnesium, molybdenum and other agriculturally usefulmetals in high enough concentration to be economically recoverable, thenthe method of recovery comprises mixing water soluble humic acid withthe water to be cleaned. The water soluble humic acid will chelate themetals to be recovered and form an insoluble humate. The insolublehumate is recovered from the water by sedimentation followed byfiltration or other separation means and is useful as a source ofchelated micronutrients for agriculture. If the agriculturally viablemetal content of the contaminated water is too low for economicrecovery, or if the metals are not useful for agriculture such as lead,chromium, mercury or the like, then a water insoluble form of humic acidcan be used. Once the humic acid has been cross-linked and itssolubility decreased, the metal ions are retained on the insolubilizedhumic acid. The cross-linked humic acid can be further insolubilized byimmobilization on a carrier such as a gel.

To prepare the absorbent according to the present invention, humic acidis purified by acid precipitation followed by dissolution in distilledwater at a pH of approximately 7. This dissolution and precipitation isrepeated, after which the precipitated humic acid is washed with asuitable buffer and filtered through an appropriate filtration device.

Alternatively, the precipitated humic acid is washed by centrifugationand resuspension of solid humic acid. After washing, the material isdried overnight at temperatures from about 60-70° C. The dried materialis then water-insolubilized, although it is still capable of adsorbingmetals or organics. The water insoluble adsorbent can be renderedsoluble by contact with monovalent metal ions.

In order to make humic acid insoluble at higher pH, the humic acid iscross-linked with conventional cross-linking agents such as aldehydecross-linking agents, e.g., glutaraldehyde, or with at least oneoxidoreductase enzyme.

The solubility of cross-linked humic acid can be lowered further and itshandling properties improved by immobilization in a solid support suchas a matrix or gel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the effect of pH on uranium removal using HUMASORB-L™according to the present invention.

FIG. 2 shows the effect of pH on removal of various metals usingHUMASORB-L™ according to the present invention.

FIG. 3(A) shows the Freundlich plot for copper sorption by HUMASORB-S™according to the present invention.

FIG. 3(B) shows the Freundlich plot for nickel sorption by HUMASORB-S™according to the present invention.

FIG. 4(A) shows the Langmuir plot for copper adsorption by HUMASORB-S™according to the present invention.

FIG. 4(B) shows the Langmuir plot for nickel adsorption by HUMASORB-S™according to the present invention.

FIG. 5 shows the Scatchard plot for copper and nickel metal sorption onHUMASORB-S™ according to the present invention.

FIG. 6 shows reduction of chromium (VI) by HUMASORB-S™ according to thepresent invention.

FIG. 7(A) shows the Freundlich isotherm for TCE adsorption onHUMASORB-S™ according to the present invention.

FIG. 7(B) shows the Langmuir isotherm for TCE adsorption on HUMASORB-S™according to the present invention.

FIG. 8(A) shows the Freundlich isotherm for PCE adsorption onHUMASORB-S™ according to the present invention.

FIG. 8(B) shows the Langmuir isotherm for PCE adsorption on HUMASORB-S™according to the present invention.

FIG. 9 shows removal of organic contaminants using HUMASORB™ accordingto the present invention.

FIG. 10 shows solubility of cross-linked (both chemically andenzymatically) humic acid as compared with pure humic acid over a rangeof pH.

FIG. 11 shows that the solubility of cross-linked humic acid can belowered by immobilizing the cross-linked humic acid.

FIG. 12 is a flow chart of the process of the present invention forconverting contaminated water to fertilizer and agriculturally usefulwater.

FIG. 13 illustrates how HUMASORB-S™ reduces chromium (VI) to chromium(III) and removes chromium from solution.

DETAILED DESCRIPTION OF THE INVENTION

Several humic acid products are available from ARCTECH, Inc. under thetrade name HUMASORB. Of these, HUMASORB-L™ is a liquid, whereasHUMASORB-S™ and HUMASORB-CS™ are solids. Humasorb-S™ dissolves in waterat elevated pH under certain conditions, such as in the presence ofmonovalent species. HUMASORB-CS™ is a cross-linked derivative ofHUMASORB-L™/HUMASORB-S™ designed to lower solubility of the humic acidat higher pH, while retaining the properties of contaminant removal.

The humic acid adsorbent of the present invention is useful inminimizing and reducing the volume of metal-, inorganic ion- andorganic-contaminated water, wastewater, and soil. The insolubilizedpurified humic acids are particularly useful in treating all types ofwater because in one step they adsorb cations and anions as well asorganic molecules, with no requirement for sludge dewatering. Ofparticular importance is that the insolubilized purified humic acid canbe used to reduce metals present as anions to the cationic state forremoval by chelation or ion exchange, e.g., Cr(VI) to Cr(III). Only onesecondary waste stream is generated. That secondary waste stream, whichis primarily composed of combustible organic materials, can be furtherreduced by thermal destruction technologies to achieve a volumereduction of 100 to less than 1.

Humic acid is a natural material with many properties which can beexploited for several cost effective applications. Humic substances arecomplex mixtures of naturally occurring organic materials. Thesesubstances are formed from the decay of plant and animal residues in theenvironment. Humic acid constitutes a significant portion of the acidradicals found in humic substances.

Humic acid is dark brown to black in color and is considered to be acomplex aromatic macromolecule with various linkages between thearomatic groups. The different compounds involved in linkages includeamino acids, amino sugars, peptides, aliphatic acids and other aliphaticcompounds. The carboxylic, phenolic, aliphatic and enolic-hydroxyl andcarbonyl are the various functional groups in humic acid. Humic acid isan association of molecules forming aggregates of elongated bundles offibers at low pHs and open flexible structures perforated by voids athigh pHs. The voids can trap and adsorb both organic and inorganicparticles if the charges are complementary.

Humic acid has a large cation exchange capacity and holds bothmonovalent and multivalent elements very strongly. The molecular weightof humic acid ranges from about 800 daltons to about 500,000 daltons,with the weight average molecular weight being from about 5000 daltonsto about 50,000 daltons. The cation exchange capacity of humic acidvaries from about 200 to about 500 meq CaCO₃ per 100 grams at pH 7,depending upon the source of the humic acid.

Humic acid is a polyelectrolyte, and is believed to form complexes withclay particles. When the cation exchange sites on the humic acidmolecule are filled predominantly with hydrogen ions, the material,which is considered to be an acid, is insoluble in water. However, whenthe predominant cations at the exchange sites are other than hydrogen,the material is called a humate. Humates of the monovalent alkali metalsor ammonia are soluble in water, but the humates of most multivalentmetals are insoluble.

The sorption of chemicals onto the surfaces of humic substances has beenstudied by a large number of environmental chemists. Sorption mechanismsare defined to include Van der Waals attractions, hydrophobic bonding,hydrogen bonding, charge transfer, ion exchange, and ligand exchange.

A major source of humic acid is coal--the most abundant and predominantproduct of plant residue coalification. All ranks of coal contain humicacid but lignites represent the most easily available and concentratedform of humic acid. Humic acid concentration of lignite varies from30-90%, depending upon location. Peat, humates and sewage sludge alsocontain significant quantities of humic acid.

actosol® is manufactured by ARCTECH, Inc. of Chantilly, Va. as a soilamendment product. actosol® is a family of products based upon humicacid extracted from low rank coals, such as leonardite. HUMASORB™,derived from actosol®, has the ability to adsorb organic material,capture metal ions, and capture radionuclides and anions. Because of thedistribution of its functional groups, humic acid has cation exchangesites needed for the chelation and removal and/or recovery of metals.The metal binding capacity of humic acid is a function of pH. Inaddition, humic acid readily removes organics from waste waters througha physical adsorption phenomenon in a fashion similar to that ofactivated carbon.

Humic acid was isolated and purified from actosol® by acidificationusing concentrated hydrochloric acid to lower the pH below about 2. Theprecipitated solids were purified by repeated washing with distilledwater and acidification. A pressure filter (60 psig) was used toseparate the precipitated humic acid from the other humic substancesdissolved in water. The amount of humic acid recovered ranged from about11.79% to about 14.79% by weight of actosol®.

Humic acid can be insolubilized by two different methods. In one method,multivalent metals are complexed or chelated to humic acid toinsolubilize the humic acid. These can be metals such as iron, aluminum,copper, manganese, lead, cadmium, mercury, chromium or other multivalentmetals. Although univalent metals such as potassium, sodium and the likeusually produce soluble complexes or chelates, when the cation is thehydronium ion (H⁺), the humic acid is insoluble in water.

The other method for producing insoluble humic acid is to polymerize orcross-link the humic acid. By cross-linking humic acid, awater-insoluble polymer is formed which lowers the solubility of theadsorbent as the pH is increased. The active groups of the humic acidare protected by calcium. The cross-linked humic acid has a lowsolubility in water after cross-linking at near neutral pH even in thepresence of sodium ions.

Any conventional cross-linking agent can be used to cross-link the humicacid to produce an insoluble product, e.g., HUMASORB-CS™. Among thecross-linking agents that can be used to produce HUMASORB-CS™ arealdehydes and oxidoreductase enzymes. These products showedsignificantly lower solubility at higher pH, as shown in FIG. 1. Forexample, when glutaraldehyde or a mixture of glutaraldehyde and mineralacid (HCl, HNO₃, H₂ SO₄, H₃ PO₄, etc.) is used, the resultingcross-linked humic acid has a low solubility in water at near neutral pHi n the presence of sodium ions.

Among the aldehydes that can be used for cross-linking humic acid arealiphatic or aromatic aldehydes having from 1 to 22 carbon atoms. Thealdehydes may be substituted with any substituent that does notadversely affect the cross-linking capabilities of the aldehydes. Thealdehydes may be saturated or unsaturated. The aldehyde may be anaromatic aldehyde, such as benzaldehyde, tolualdehyde (o-, m-, or p-) orsalicylaldehyde.

Any type of oxidoreductase enzyme can be used to cross-link the humicacid, including peroxidases and hydrogenases.

The cross-linking is effected by reacting the humic acid with thealdehyde or oxidoreductase enzymes such as peroxidase enzymes at roomtemperature or slightly above room temperature for a period of two tofive hours.

Not only does HUMASORB-CS™ retain the metal sorption capacity of humicacid after cross-linking, the metal sorption capacity of humic acid isgreatly increased by virtue of the cross-linking.

In order to lower the solubility of cross-linked humic acid evenfurther, the cross-linked humic acid can be immobilized within a solidsupport, such as a gel or other matrix. Both soluble humic acid andinsoluble (i.e., cross-linked) humic acid can be immobilized. Any typeof inert gel/matrix or other insoluble material can be used to form asolid support for the humic acid adsorbent. Among the types ofentrapment media which can be used are alginates, cross-linked dextrangels, agar, gellan, chitosan and curdlan. Other types of supports can beused to immobilize the humic acid adsorbent, including supports used formicroorganisms in fermentation processes which are well known to thoseskilled in the art. Among these immobilizing supports are polystyrenebeads, acrolein beads, and the like. The support, of course, does notenter into the adsorption process, but merely suspends the adsorbent inthe liquid to aid the adsorbent's contacting the contaminants to beadsorbed.

The preferred matrix for immobilizing any form, solid or liquid, ofhumic acid is a gel, such as calcium/alginate matrix/gel. Theimmobilization process produces beads of immobilized humic acidadsorbent encapsulated in a calcium/alginate matrix/gel which has asignificantly lower solubility than the un-immobilized humic acid. Whenthe immobilized HUMASORB™ is contacted with the contaminated water, thecontaminated water diffuses through the matrix to contact the HUMASORB™.Although there may be some diffusion limitations, these are expected tobe negligible. The immobilized product was found to be effective inremoving Cr⁺³ from simulated waste streams in both batch and columnstudies. The solubility characteristics of the immobilized product arecompared with other forms of humic acid adsorbent in FIG. 10.

For treating water containing agriculturally desirable metals accordingto the present invention, soluble humic acid, such as HUMASORB-L™, isadmixed with water. When the humic acid contacts the multivalent metalsin solution, an ion exchange complexation reaction occurs, chelating themultivalent metals. The multivalent metal chelated complex is insolublein water and coagulates, settling out as a floc.

The soluble humic acid, such as HUMASORB-L™, can be used todecontaminate soils and various structural materials and equipment. Thedecontamination is easily accomplished by rinsing the contaminated soilor equipment with HUMASORB-L™ and separating the spent HUMASORB-L™.Similarly, contaminated structural materials can be washed withHUMASORB-L™ to remove the contaminants. The spent HUMASORB-L™ from theseoperations can be further precipitated and separated for final disposal.

Soluble humic acid, such as HUMASORB-L™, can be used to recoverdesirable metals for use as fertilizers. A study was conducted torecover micronutrients and remove toxic metals such as cadmium using atwo-step process based upon HUMASORB-L™. This study was conducted usingcontaminated water from a Superfund Site, which was representative ofacidic water with large quantities of heavy metals dissolved therein. Aspart of this study, micronutrients recovered from the contaminated waterwere used in a fertilizer composition marketed as actosol® by ARCTECH,Inc.

EXAMPLE 1

In the study to remove heavy metals such as cadmium from contaminatedwater, an actual field waste stream was treated. Using the adsorbentaccording to the present invention HUMASORB™, nearly 98% of the copperand iron in the contaminated water was captured for use as fertilizermicronutrients, and significant percentages of other micronutrients suchas zinc, manganese, and magnesium were captured as well. Toxic heavymetals such as cadmium and arsenic were removed to levels below thedetection limit of standard laboratory tests before the water wasdischarged. Table 1 shows a comparison of the metals present in thecontaminated water before and after the treatment was conducted:

                  TABLE 1                                                         ______________________________________                                                      Raw Water Treated Water                                         Metals        (ppm)     (ppm)                                                 ______________________________________                                        Aluminum      255       7.87-B                                                Arsenic       0.513     0.151-U                                               Cadmium       1.99      0.0715-B                                              Copper        198       0.287-B                                               Iron          982       0.602-B                                               Magnesium     417       271                                                   Manganese     195       52.4                                                  Potassium     9.21-B    3990                                                  Zinc          555       48.1                                                  ______________________________________                                         B: Below method detection limit                                               U: Undetected                                                            

As shown in Table 1, aluminum, arsenic, cadmium, copper and iron wereeither undetected or below the method detection limit. The increase inthe concentration of potassium in the treated water is believed to bedue to the exchanges of metals in the contaminated water with potassiumpresent in HUMASORB-L™. This treatability study demonstrated thatadsorbent of the present invention is useful for treatment and resourcerecovery of acidic, heavy metal laden waters. The soluble humic acidproduct of the present invention can be used to tie up contaminants inthe water, such as heavy metals. FIGS. 1 and 2 show the use ofHUMASORB-L™ to remove barium, uranium, cadmium, copper and nickel fromwater.

For treating waters that do not contain sufficient amounts ofagriculturally desirable metals to make it economically feasible toattempt recovery of such metals, or if the water contains undesirablemetals or organic contamination, or both, insoluble cross-linked humicacid is used and the contaminated water is passed through a column ofthe adsorbent of the present invention to remove the undesiredcontaminants.

For treating waters containing agriculturally desirable metals, theHUMASORB-L™ is mixed with the metal containing water. When the humicacid contacts the metals in solution, an ion exchange/complexationreaction occurs. Insoluble humates are formed which are then recoveredas chelated micronutrients by sedimentation followed by filtration. Theamount of HUMASORB-L™ to use will vary depending on the concentration ofdesirable metals in the contaminated water, and must be determined byexperimentation. The amount of HUMASORB-L™ to be used can readily bedetermined by one skilled in the art without undue experimentation. Theadsorbent of the present invention treats organics, metal ions andanions in a single process step. When the adsorbent is used to treatwaters containing agriculturally useful metals or micronutrients, theproducts of the treatment are marketable as a soil amendment product.When the adsorbent of the present invention is compared to carbonadsorption and ion exchange resins in terms of performance and costsavings, the adsorbent of the present invention is the method of choice.

For treating waters that do not contain sufficient amounts ofagriculturally desirable metals, or if the water contains undesirablemetals or organic contamination, insoluble (i.e., cross-linked) humicacid (e.g., HUMASORB-CS™) is used and the contaminated water is passedthrough a column of the insoluble adsorbent.

The adsorbent of the present invention is useful in removing metal ionssuch as Fe³⁺, Al³⁺. Cr³⁺, Pb²⁺, Cu²⁺, Zn²⁺, Co²⁺, Hg⁺, Cd²⁺, Ni²⁺, andMn²⁺, either singly or together. Because the adsorbent of the presentinvention also adsorbs organics and removes metals present as anions aswell as cations, no separate treatment with activated carbon or with ananion exchange resin is required to remove all contaminants from thematerial treated.

Precipitates formed between metal ions and the adsorbent of the presentinvention are compact and noncolloidal. The volume of their sludge issharply reduced in comparison to that of finely dispersed calcium oxideprecipitates, which have conventionally been used for treating wastestreams. Therefore, it is easy to remove the precipitates formed byadsorbents of the present invention by simple filtration or settling. Ifit is desired to recover the metal values sequestered in the adsorbent,it is possible to elute these metal values from the precipitates with anappropriate acid. This is not possible with conventional calcium oxideprecipitation of heavy metals.

The humic acid based adsorbent of the present invention may be used ineither soluble or insoluble form, either alone or in admixture withother forms of humic acid according to the present invention. Anionssuch as nitrate or nitrite or similar anions are weakly adsorbed due tothe charged nature of the humic acid molecule and the multitude ofactive (charged) sites. Although adsorption according to the presentinvention is not governed by any one theory, it is believed that organicmolecules are adsorbed because of the oleophilic nature of the humicacid molecule. In other words, it is believed that the organic moleculesadsorbed partition onto the "organic like" surface of the humic acidmolecule.

EXAMPLE 2

Water contaminated with benzene was treated with soluble humic acid(HUMASORB-L™) in a 125 ml serum vial with a ratio of 4.16676 ml actosol®per ml of spiked water (i.e., approximately 1 gram of humic acid per mgof benzene). The benzene-contaminated water was contacted withHUMASORB-L™ was at room temperature for approximately two hours. Aftertwo hours, the benzene was completely removed from the water. Thebenzene- containing HUMASORB-L™ separated from the water by coagulationwith alum followed by filtration.

Metal Sorption

The effect of pH on the sorption of metals by HUMASORB-L™ was evaluatedby adjusting the pH with sodium hydroxide (1.0N) or concentratedhydrochloric acid (1.0N). In polypropylene centrifuge bottles,HUMASORB-L™ was contacted with spiked water solution containing knownconcentrations of metals. The spiked solutions were prepared bydissolving the metal salts in water. The centrifuge bottles were shakenat 300 rpm and 25° C. for the desired contact time. After the desiredcontact time, 10% alum solution was added to the centrifuge bottles tocoagulate humic acid. The bottles were then centrifuged at 2000 rpm for30 minutes to separate the solid and liquid phases. The supernatant inthe bottles was analyzed for the target metal.

The desired contact time for all of these processes is the time neededto obtain equilibrium conditions. It has been determined that formetals, this time is approximately two to three hours, and for organics,the time to reach equilibrium is about 24 hours.

The adsorption capacity of purified humic acid was evaluated bydeveloping metal sorption isotherms. The spiked water solution wascontacted with different amounts of humic acid in centrifuge bottles.The pH was not adjusted in these tests. The centrifuge bottles wereshaken at 300 rpm and 25° C. for two hours. After the desired contacttime, the bottles were centrifuged at 2000 rpm for 30 minutes toseparate the solid and liquid phases. The ability of humic acid toreduce toxic metals such as Cr (VI), present as anions (Cr₂ O₇)⁻², toless toxic Cr(III) was also evaluated in a similar manner.

EXAMPLE 3

HUMASORB™ was immobilized further to reduce solubility and improvehandling properties. The different forms of HUMASORB™ were immobilizedin calcium-alginate matrix/gel. The adsorbents were immobilized both inthe presence and absence of glutaraldehyde, a cross-linking agent.Immobilized HUMASORB™ was then evaluated for removal of chromium, arepresentative target contaminant from simulated waste streams.

In this study, the initial chromium concentration was 200 ppm. Thesimulated waste stream was contacted with the adsorbent for two hours at25° C. and 300 rpm. The adsorbent loading was 0.5 grams in 25 mlcontaminated water. All of the adsorbents tested were immobilized incalcium-alginate matrix/gel. The results of this study and the pH areshown in Tables 2 and 3.

                  TABLE 2                                                         ______________________________________                                        Chromium Removal Using Immobilized HUMASORB ™                              Adsorbent.sup.++  Percent Removal                                                                           pH                                              ______________________________________                                        HUMASORB-L ™   81.06       5.07                                            HUMASORB-L ™   82.37       5.22                                            HUMASORB-L ™/Glu**                                                                           60.69       4.51                                            HUMASORB-L ™/Glu**                                                                           66.24       4.54                                            HUMASORB-S ™   30.20       2.89                                            HUMASORB-S ™   12.24       2.87                                            HUMASORB-S ™/Glu**                                                                           49.14       2.95                                            HUMASORB-S ™/Glu**                                                                           37.49       2.95                                            Calcium-alginate (control)                                                                      49.20       3.95                                            Calcium-alginate (control)                                                                      41.63       3.99                                            ______________________________________                                         .sup.++ All adsorbents immobilized in calciumalginate matrix/gel              **Glutaraldehyde                                                              Reaction conditions:                                                          Initial chromium concentration: 200 ppm                                       Contact time: 2 hrs at 25° C. and 300 rpm                              Adsorbent loading: 0.5 grams in 25 ml contaminated water.                

                  TABLE 3                                                         ______________________________________                                        Chromium Removal Using Immobilized HUMASORB ™ Over Time                    Time (Hours)   Percent Removal                                                ______________________________________                                        2              89.01                                                          4              97.39                                                          8              97.61                                                          16             100                                                            ______________________________________                                         Reaction Conditions:                                                          Initial chromium concentration: 200 ppm                                       Contacted at 25° C. and 300 rpm; pH: 5-5.5                             Adsorbent: HUMASORBL ™/Glutaraldehyde (Immobilized in calciumalginate      matrix/gel)                                                                   Adsorbent loading: 0.5 grams in 25 ml contaminated water                 

Several of the adsorbents were used in additional experiments conductedin succinate buffer to keep the pH relatively constant and todemonstrate that the differences in pH were not primarily responsiblefor increased chromium removal with immobilized HUMASORB™. In addition,silica gel, a relatively inert material, was also immobilized, usingcalcium-alginate matrix/gel for comparison. In the first study, theresults of which are shown in Table 4, the adsorbent loading was 0.5grams of adsorbent in 25 ml contaminated water. The contact time was twohours at 25° C. and 300 rpm. In the second study, the results of whichare shown in Table 5, the adsorbent loading was 0.5 grams in 25 mlcontaminated water, and the contact time was twelve hours at 25° C. and300 rpm.

                  TABLE 4                                                         ______________________________________                                        Chromium Removal Using Immobilized HUMASORB ™                              (in Succinate Buffer)                                                                                      Chromium                                                        Initial                                                                              Final  Concentration                                                                          Percent                                 Adsorbent      pH     pH     (ppm)    Removal                                 ______________________________________                                        Control (chromium solution)                                                                  5.0    4.87   196.58   --                                      Calcium alginate beads                                                                       5.0    4.96   183.04   6.89                                    Silica gel/Ca-alginate                                                                       5.0    5.03   178.11   9.40                                    HUMASORB-S ™/Ca-                                                                          5.0    4.72   164.32   16.41                                   alginate                                                                      HUMASORB-L ™/Glu/Ca-                                                                      5.0    5.30   157.47   19.90                                   alginate                                                                      ______________________________________                                         Reaction Conditions:                                                          Adsorbent loading: 0.5 grams in 25 ml contaminated water                      Contact time: Two hours at 25° C. and 300 ppm (in succinate buffer

                  TABLE 5                                                         ______________________________________                                        Chromium Removal Using Immobilized HUMASORB ™                              (Longer Contact Time) (In succinate buffer)                                                                Chromium                                                        Initial                                                                              Final  Concentration                                                                          Percent                                 Adsorbent      pH     pH     (ppm)    Removal                                 ______________________________________                                        Control (chromium solution)                                                                  5.26   5.31   197.25   --                                      Calcium alginate beads                                                                       5.16   5.06   158.0    19.90                                   Silica gel/Ca-alginate                                                                       5.15   5.08   174.9    11.33                                   HUMASORB-L ™/Glu/Ca-                                                                      5.23   5.84   115.6    41.39                                   alginate                                                                      ______________________________________                                         Reaction Conditions:                                                          Adsorbent loading: 0.5 grams in 25 ml contaminated water                      Contact time: 12 hours at 25° C. and 300 rpm (in succinate buffer)

The results of these experiments shown in Tables 4 and 5 clearlyindicate that immobilized HUMASORB™ is more effective than thecalcium-alginate beads (control), and silica gel immobilized usingcalcium-alginate beads. The lower removal of chromium in succinatebuffer is believed to be due to sodium in the succinate buffer competingfor sites in the adsorbent.

Organic Adsorption

Isotherms for adsorption of chlorinated and petroleum hydrocarbons weredeveloped using HUMASORB-S™. Initial experiments were conducted usingHUMASORB-L™. The chlorinated hydrocarbons used were trichloroethylene(TCE) and tetrachloroethylene (PCE); benzene was the representativepetroleum hydrocarbon used in this study.

Isotherms were developed by contacting spiked water samples withdifferent amounts of humic acid in a 20 ml serum vial. HUMASORB™ wasground to less than 325 mesh when used in solid form in the experiments.The spiked water solution and the HUMASORB™ were contacted incrimp-sealed vials at 350 rpm and 251 for the desired time. The vialswere centrifuged at 2000 rpm for 30 minutes after the contact time toseparate the liquid and solid phases. The liquid phase was analyzed byusing purge and trap GC- MS. The experimental procedure was similar forall forms of HUMASORB™, liquid or solid.

Metal Sorption

The effect of pH on uranium removal using HUMASORB-L™ humic acid isshown in FIG. 1. Clearly, the results indicate that HUMASORB-L™ is veryeffective removing uranium from water under acidic conditions. Uraniumis soluble in water under acidic conditions, and increasing the pH to 4using NaOH results in only 6% removal of uranium. Uranium is completelyremoved from the solution at pHs greater than 6.

However, at pH 4, the addition of HUMASORB-L™ removed all of the uraniumfrom solution and the uranium was recovered as a solid bound to humicacid. The recovery of uranium decreased at higher pH in the presence ofhumic acid. The observed decrease in uranium recovery at higher pH inthe presence of humic acid is expected, as humic acid dissolves in waterat higher pH levels. The comparison of uranium recovery both in theabsence and presence of HUMASORB-L™ indicates that uranium is bound tohumic acid over the pH range of 2-12 and remains in solution under basicconditions in the presence of humic acid. The addition of a coagulantsuch as alum did not have a significant effect at higher pH. However, atnear neutral pH(6-8), the addition of alum increased the amount ofuranium recovery from water. The effect of pH on the removal ofdifferent metals using HUMASORB-L™ is shown in FIG. 2.

The sorption of copper and nickel by purified humic acid (HUMASORB-S™)was represented well by both the Freundlich and Langmuir models (FIGS. 3and 4). The Langmuir model for nickel, however, gave negative values forthe constants. However, the sorption of cadmium did not follow eitherthe Freundlich or the Langmuir model indicating a complex multilayersorption.

The metal sorption data were also analyzed using the method developed byScathard in Ann. New York Acad. Sci. 51:660-672 (1949). The presence ormore than one inflection point on a plot based on Scatchard analysisusually indicates the presence of more than one type of binding site.The Scatchard plot for the sorption of different metals by humic acid isshown in FIG. 5. The plot clearly indicates the presence of more thanone type of binding site for copper and nickel sorption. The plot was,however, linear for cadmium, indicating that possibly only one type ofbinding site was active for cadmium sorption.

Humic acid can act as a reducing agent and influence oxidation-reductionof metal species. An unchelatable toxic oxo-anion such as chromiumpresent as dichromate (Cr₂ O₇)⁻² is reduced to relatively non-toxicCr(III). The reduced chromium is then stabilized through chelation byhumic acid. The reduction of different metal species such as mercury,vanadium, ion and plutonium by humic acid has been reported by a numberof investigators (Alberts, J. J. et al., Science 184:895, 1974; Szalay,A. et al., Geochim. Cosmochim Acta. 1:31, 1967; Theis, T. L. et al.,Trace Met. Met-Org. Interact. Nat. Waters. [Symp.], 273, 1976;Bondiette, E. A. Transuranium Nuclides Environ., Proc. Symp. 273, 1976).

The purified soluble humic acid (HUMASORB-S™) used in the present studywas able to reduce Cr(VI) completely as shown in FIG. 6.

FIG. 13 shows the concentration of both Cr(VI) and Cr(III) duringtreating water containing Cr(VI) with HUMASORB-S™. FIG. 13 clearly showsthat the total chromium concentration decreases during the reaction,indicating that Cr(VI) is reduced and the resulting Cr(III) is removedimmediately. The removal of Cr(III) is believed to be by a combinationof ion-exchange and complexation.

Freundlich and Langmuir adsorption models used to represent the dataobtained for adsorption of organic compounds. The data for TCEadsorption was not represented by either model (FIG. 7). The isothermsshow two distinctive phases with adsorption capacity increasing onlyslightly with concentrations up to 210 ppm and increasing rapidly above210 ppm. The shape of the isotherm indicates the possibility ofmulti-layer adsorption, with adsorption capacity increasing rapidly athigher concentration.

The adsorption of PCE on HUMASORB-S™ was also represented well by bothFreundlich and Langmuir models as shown in FIG. 8. However, the Langmuirmodel gave negative values for the constants. The Freundlich andLangmuir model parameters determined from the isotherms for some of thecontaminants evaluated herein are shown in Table 6.

                  TABLE 6                                                         ______________________________________                                        Freundlich and Langmuir Model Parameters                                      Contaminant                                                                              Freundlich     Langmuir                                            ______________________________________                                        Copper     K = 0.4064 mg/gm                                                                             K = 142.91 mg/gm                                               n = 1.0218     b = 0.0029 l/mg                                     Nickel     K = 0.0300 mg/gm                                                                             Negative Values                                                n = 0.7500                                                         PCE        K = 0.07691 mg/gm                                                                            Negative Values                                                n = 0.6697                                                         ______________________________________                                    

Benzene adsorption on HUMASORB-S™ was represented very well by both themodels at the relatively higher equilibrium concentrations obtainedherein. The removal of PCE from spiked water was higher compared to theremoval of both TCE and benzene under the conditions used for thedevelopment of the adsorption isotherms. However, removal of both TCEand benzene increased significantly with the increase in the amount ofHUMASORB-S™, as shown in FIG. 9.

The adsorption of trichloroethylene (TCE) by humic acid was alsoevaluated using HUMASORB-L™ in the same manner and ratio as for benzene.TCE removal was only 55% at the end of two hours contact time, butremoval increased to 61% with a contact time of 18 hours. The removalincreased to 94% at the end of two hours when insoluble, acidified,purified humic acid (HUMASORB-S™) was used.

Accordingly, either soluble humic acid or insolubilized humic acidadsorbent, alone or together, can be used to remove organic contaminantsfrom water by treating the water with the appropriate form of humic acidadsorbent and letting the water remain in contact with the humic acidadsorbent for a time sufficient to remove the organic contaminant. Thetime required to approximate equilibrium conditions for organiccontaminants can be up to 24 hours.

Remediation of contaminated streams and groundwater has beentraditionally approached with at least a two-step process including somecombination of activated carbon and ion-exchange process. Removal ofheavy metals from contaminated water has traditionally been accomplishedby techniques such as adding a precipitating agent, ion-exchange orreverse osmosis. These techniques require considerable capitalinvestment and, in addition, may require pretreatment in some case toremove oil and suspended solids.

The humic acid based adsorbent (HUMASORB™) of the present invention,which is derived from naturally occurring materials, can alleviate manyof the limitations of the conventional remediation efforts into a singlestep process. The humic acid based adsorbents of the present inventioncan be used for groundwater cleanup both in situ and in a pump and treatprocess. The parameters for the cleanup process depend upon theparticular contaminants and their concentration in the stream treated,and can be readily discerned by one skilled in the art without undueexperimentation.

Contaminated groundwater is treated by using cross-linked humic acid(HUMASORB-CS™) placed into a cartridge or a trench. In this case thehumate removes both metal ions and organics from the water in one step.If the water to be cleaned contains no monovalent ions to be removed,then humic acid made insoluble by complexing with multivalent metal ionsmay be used.

A cross-linked humic acid based adsorbent was used to treat a simulatedwaste stream containing both inorganic and organic contaminants in bathmode. The results shown in Table 7 clearly demonstrate that thecross-linked humic acid based adsorbent, HUMASORB-CS™) is very effectivefor remediation of water containing different types of contaminants.

                  TABLE 7                                                         ______________________________________                                        HUMASORB ™ IS EFFECTIVE FOR RADIONUCLIDE AND                               METAL REMOVAL FROM DIFFERENT MATRICES.sup.1                                                        Waste Stream from a                                              Simulated Waste.sup.2                                                                      Superfund Site.sup.3                                             Concentration (ppm)                                                                        Concentration (ppm)                                      Mixed Waste Stream Containing Multiple Metals                                 and Chlorinated Organics                                                                              Removal           Removal                             Contaminant                                                                             Initial                                                                              Final  %      Input                                                                              Output                                                                              %                                   ______________________________________                                        Chromium (III)                                                                          88     <0.5   >99    --   --    --                                  Copper    98     <0.5   >99    --   --    --                                  Lead      18     <0.5   >97    --   --    --                                  Trichloroethylene                                                                       140    1      99.29  --   --    --                                  (TCE)                                                                         Perchloroethylene                                                                       26     N.D.   >99    --   --    --                                  (PCE)                                                                         ______________________________________                                         .sup.1 Source of Data: ARCTECH, Inc. 14100 Park Meadow Drive, Chantilly,      Virginia.                                                                     .sup.2 Simulated waste stream with three metal and two chlorinated organi     contaminants present.                                                         .sup.3 Treatability study using actual waste stream with multiple metals      present.                                                                      N.D. Not Detected                                                        

Alternatively, if it is not possible or desirable to elute the heavymetals and regenerate the adsorbent, the dried metal sequestrates can becombusted for process heat. The heavy metals are then concentrated inthe combustion ash for recovery or disposal.

The process of the present invention provides a cost effective, one stepprocess for treating mixed wastes containing organic compounds, metalsand radionuclides. This one step process accomplishes the regulatoryrequirements for the treatment of EPA-classified priority pollutantsresulting in a several fold reduction in the volume of the contaminatedmaterials. The byproduct of the process is dry and is easily disposable.Alternatively, metals chelated by the process can be recovered byeluting under acid conditions. Alternatively, the metals can be madeinto a marketable, chelated, micronutrient agricultural product.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingcurrent knowledge, readily modify and/or adapt for various applicationsuch specific embodiments without departing from the generic concept,and therefore such adaptations and modifications are intended to becomprehended within the meaning and range of equivalents of thedisclosed embodiments. It is to be understood that the phraseology orterminology herein is for the purpose of description and not oflimitation.

The means, materials, and steps for carrying out various disclosedfunctions may take a variety of alternative forms without departing fromthe invention. Thus, the expressions "means to . . . " and "means for .. . ", or any method step language as may be found in the specificationabove or the claims below, followed by a functional statement, areintended to define and cover whatever structural, physical, chemical orelectrical element or structure, or whatever method step, which may nowor in the future exist which carries out the recited function, whetheror not precisely equivalent to the embodiment or embodiments disclosedin the specification above, i.e., other means or steps for carrying outthe same function can be used; and it is intended that such expressionsbe given their broadest interpretation.

All references cited in this specification are hereby incorporated byreference.

What is claimed is:
 1. A method for insolubilizing humic acid comprisingcross-linking solubilized humic acid.
 2. The method according to claim1, wherein the humic acid is cross-linked by contacting said humic acidwith a cross-linking agent.
 3. The method according to claim 2, whereinthe cross-linking agent is selected from the group consisting ofaldehydes and at least one oxidoreductase enzyme, and mixtures thereof.4. The method according to claim 3, wherein said cross-linking agent isglutaraldehyde or a mixture of glutaraldehyde and a mineral acid.
 5. Anadsorbent comprising insolubilized humic acid immobilized on a solidsupport.
 6. A method for insolubilizing humic acid comprising complexingor chelating multivalent metals to humic acid wherein the multivalentmetals are selected from the group consisting of lead, cadmium, mercury,chromium, aluminum, iron, copper, and manganese.
 7. An absorbentcomprising insolubilized humic acid immobilized on a solid supportwherein the solid support used to immobilize the humic acid is selectedfrom the group consisting of alginates, cross-linked dextran gels, agar,gellan, chitosan, and curdlan.
 8. An absorbent comprising insolubilizedhumic acid immobilized on a solid support wherein the solid support usedto immobilize the humic acid is selected from the group consisting ofpolystyrene beads and acrolein beads.
 9. An adsorbent comprisinginsolubilized humic acid immobilized on a solid support wherein thesolid support used to immobilize the humic acid is a calcium/alginatematrix gel.